The present invention relates to apparatus and methods for delivery of topical anesthetics and refrigerants, hereinafter collectively referred to as vapocoolants. More particularly, the apparatus comprises containers, associated valve arrangements and, optionally, filters that provide a long shelf life and maintain delivery characteristics over the shelf life in a manner suitable for pharmaceutical applications. The apparatus operates over a range of pressure commonly encountered in medical applications to provide substantially uniform delivery of vapocoolant. The apparatus may be constructed to provide either a stream or a mist delivery.
Preferred vapocoolants include ethyl chloride, ethyl chloride-fluorocarbon blends, fluorocarbon fluids and blends of fluorocarbon fluids such as 15% dichlorodifluoromethane and 85% trichloromono-fluoromethane. Also, non-halogen containing low boiling fluids suitable for topical skin application may be used. The vapocoolant will typically operate as a self-propellant by providing a suitable pressure for discharge in a vapor space above the liquid supply of vapocoolant. However, an inert gas such as nitrogen may be combined with the vapocoolant to achieve modified discharge characteristics. For convenience, the invention is described hereinafter with particular reference to ethyl chloride.
Ideally, the containers and associated valve arrangements for ethyl chloride should have a shelf life of three years and meet United States Pharmacopoeia (“USP”) specifications as well as standard aerosol requirements for functionality. As discussed more fully below, certain medical applications also require unique jet stream characteristics over the life of the product. The USP specification for residue in ethyl chloride is 100 ppm.
Heretofore, valve-actuated spray bottles and so-called metal tube containers have been used for delivery of stream and mist flows of vapocoolant. Although such apparatus have provided effective delivery, they have not been entirely satisfactory. More particularly, it has not been possible to economically modify the prior art apparatus to comply with current FDA regulations and commercial production standards. Most notably, undesirable rates of product lost due to valve leakage have been experienced in connection with bottle apparatus. Although the metal tube apparatus provides substantially satisfactory performance, the cost of this delivery system including its threaded valve actuator is not economically attractive.
A current metal can spray system having a button actuated valve has not complied with contaminant or residue standards. That is, the vapocoolant within the spray can contains dissolved or dispersed contaminants believed to result from the solvent action of the vapocoolant on internal polymeric components of the spray can.
The vapocoolants may be used in topical application procedures requiring precise control of the area of skin contacted by the applied stream. For example, treatment of certain myofascial pain syndromes with vapocoolant in combination with stretching procedures may inactivate a trigger point and relieve the patient's pain. A discussion of myofascial pain and myofascial trigger points is provided in the International Rehabilitation Medicine Association monograph, Myofascial Pain Syndrome Due to Trigger Points, by David G. Simons M. D., November 1987, incorporated herein by reference. One specific myofascial therapy is the stretch and spray method of treatment which permits gradual passive stretch of the muscle and inactivation of the trigger point mechanism. To that end, a jet stream of vapocoolant is applied to the skin in one-directional parallel sweeps. Initially, one or two sweeps of spray precede stretch to inhibit the pain and stretch reflexes. The spray of vapocoolant is applied slowly over the entire length of the muscle in the direction of and including the referred pain zone. As described, the stream flow and size characteristics together with precise positioning of the vapocoolant along the muscle being treated is important to achieve inactivation of the trigger point mechanism.
In such procedures, a stream delivery of relatively small dimension is preferred. For example, the diameter of the stream at the valve nozzle may be in the range of several thousandths of an inch, e.g., from about 0.004″ to about 0.015″. Preferably, the delivery flow is stable and the stream configuration is sufficiently maintained to achieve the desired skin contact area with the valve nozzle being positioned up to about 10 or 15 inches from the patient.
In order to achieve such stream stability, the fluid delivery components of the container must not be affected excessively by changes in pressure that occur with change of container orientation during stream application and reduction of the vapocoolant supply within the container during the application life of the container, i.e. the time period within which the container is periodically used before emptied of vapocoolant. Similarly, the button valve itself must receive the flow of vapocoolant from the supply thereof within the container and establish satisfactory fluid flow characteristics prior to the exit of the fluid from the nozzle opening.
The achievement of a fine jet stream requires a nozzle having a highly uniform orifice or opening that is free of dimensional irregularities. For example, a nozzle opening having a diameter of about 0.005″ preferably has a size tolerance of ±0.0005″ along a length in the order of 0.02″.
The reliable provision of such jet stream flows has heretofore been inhibited by the presence of contaminants which may result from in situ formed solid residues or derived from the spray apparatus including the container, valve, actuator and/or flow passage surfaces contacted by the vapocoolant. Such contaminants may partially block or otherwise sufficiently inhibit or alter flow through the nozzle discharge bore and/or opening so as to prevent the achievement of the desired jet stream. Such contaminants may result from plastic dip tubes and actuator elements that retain manufacturing debris of extremely small size, e.g., elongated flash debris having a 0.0005″ diameter and a 0.010″ length. Cleaning techniques including washing and vacuum removal are economically undesirable and often not sufficiently reliable.